Certain types of earth-moving and excavating machinery are equipped with digging buckets (having digging teeth facing toward the machine) or dippers (having teeth facing away from the machine) capable of holding anywhere from a fraction of a cubic yard to several cubic yards of material. As used in this specification, the term "bucket" is a general term referring to a bucket, a dipper or to any other type of scoop-like device attached to a machine for digging.
One type of digging machine is called a dragline and uses a large, cable-suspended digging bucket. Such draglines are often used in strip mining to remove "overburden" material covering, e.g., coal or ore, and to remove the product being mined. A dragline may be crawler mounted and very large draglines are often configured as what is known as a "walking" dragline, so named because of the leg and foot-like mechanisms used to move it short distances.
Digging is by lowering the bucket onto the material to be removed and dragging the bucket toward the machine. As the bucket is drawn toward the machine, its digging teeth bite into the material and the bucket fills. After the bucket is filled, the boom is swung laterally and the bucket tipped for dumping the load.
Other types of digging machines such as front end loaders, back hoes, hydraulic excavators, mining shovels and the like are also equipped with digging buckets and sometimes such buckets are of very substantial capacity. Unlike the bucket of a dragline, the bucket of a front end loader is attached to and manipulated by two or three rigid arm-like members which are manipulated by hydraulic cylinders.
A large bucket, particularly a dragline bucket, often has a bucket lip to which is attached various components to protect the lip and to dig. More specifically, such a bucket has several tooth assemblies mounted in spaced-apart relationship along the lip. Lip shrouds are positioned between the tooth assemblies to protect the lip. The reason for the shrouds is that the lip is a very expensive equipment component to replace (especially in larger buckets) and the shrouds and components of the tooth assemblies are considered as expendable replacement parts.
To give some idea of size, the tip of a digging tooth for a large bucket may have a length of 13 inches or so (as measured in the direction of digging), a width of about 12 inches and weigh about 160 pounds. And a large bucket itself may weight several thousand pounds. The lip shrouds are correspondingly large.
More specifically, each hollow, sheath-like tip is fitted over and supported by a tooth "nose" or base. The tip (which is generally hollow to receive the base) has a pair of apertures, one each in the top and bottom tip plate. The base has a single vertical aperture. When the tip is fully seated on the base and in tip-supporting contact therewith, the apertures are aligned and form a single vertical "top-to-bottom" aperture.
Conventional digging tooth assemblies are retained on the lip (or, in the case of a tooth assembly, on a base piece) by a wedge pin alone or by a wedge-shaped member used with a wedge pin. Such member is sized so that when in place, a small aperture remains.
A wedge-shaped pin is driven (often with a sledge hammer) into such aperture and retains the shroud or the tip in place solely by friction. Such arrangement is configured in anticipation of periodic tip and/or wedge pin replacement. Examples of digging buckets and ways to retain components thereon are shown in U.S. Pat. Nos. 4,414,764 (Johansson et al.), 4,782,607 (Frisbee et al.), 4,136,469 (Zepf) and others.
Another approach to retention of tooth parts involves a cylindrical lock pin with a retaining ring (which resembles a snap ring) surrounding the pin. The apertures through which such pins are inserted are often formed by casting the part (e.g., a tooth tip) rather than by machining such apertures. As is known, casting "tolerances" are much more liberal than machining tolerances.
The conventional wedge pin arrangement is attended by a number of disadvantages. One is that, over time, the wedge pins are knocked out or they can simply become loose and fall out. The retained piece, e.g., a tooth tip, then falls off and is likely to be lost. Not only are these parts expensive to replace, their entry into auxiliary equipment, e.g., crushers, can badly damage such equipment. Another disadvantage is that the wedge pin is usually hardened and hammering such pin may cause it to splinter, sending shards of metal flying like shrapnel.
Yet another disadvantage is that the hardened wedge pin lacks significant resilience or ductility and, with slight wear, this fact promotes pin loosening. In other words, the parts are not self-adjusting to any significant degree.
Even if the wedge pin remains secure over the life of the tip, pin removal preparatory to replacement of the tooth tip is a substantial task. Because such pins are driven from the top downward, they must be removed by driving them upward using a hammer and drift pin which may not be readily available.
And to knock out the wedge pin, access to the underside of the bucket is required--a bucket weighing several thousand pounds presents an imposing "positioning task." If the digging edge of the bucket is merely lifted away from the ground (rather than totally inverting the bucket), an individual is required to work beneath the lifted bucket and this presents unnecessary risks.
Some wedge pin arrangements involve an aperture extending horizontally across the width of the tooth tip and tooth base. In theory, wedge pins should then be removable without gaining access to the bottom of the bucket. However, there is sometimes too little space between tooth assemblies to permit either satisfactory wedge pin driving or later pin removal.
A disadvantage of the cylindrical pin arrangement is that, because of aperture tolerances, the cylindrical pin may not result in a tight, wedged fit. As a consequence, there will be some "play" between parts, e.g., between the pin and the base nose. This results in wear which, with the advent of the invention, is unnecessary.
Reduction in downtime of a digging machine--as by addressing some of the disadvantages noted above--is not a trivial matter. Depending upon machine size and other factors, downtime may cost the machine owner hundreds if not thousands of dollars per hour in overhead costs.
An improved device for retaining a digging component such as a tooth tip which avoids drive pins, which eliminates a need for clear access to the bottom of the bucket and which retains the member by means other than merely friction would be an important advance in the art.